The present invention generally relates to a new valve guide for use in an exhaust valve system. Specifically, the invention is directed to a valve guide that maintains the temperature of its surface in order to prevent condensation of acidic gases, and thereby corrosion, of the valve and the valve guide. Additionally, the present invention is directed towards a method of maintaining the surface temperature of the valve guide in order to prevent corrosion.
It is known in the art relating to internal combustion engines, such as diesel engines (e.g., locomotive diesel engines), to actuate two adjacent valves of an engine cylinder by a rotating cam. For example, in FIG. 1, the cam 154 includes a select shape which determines the timing of valve 104 actuation. In order to open the valves 104, the cam 154 rotates until a cam lobe 156 engages a roller 158 located on a rocker arm 152. Once the cam lobe 156 engages the rocker arm 152, the rocker arm 152 in turn engages a valve bridge 160, which causes compression in adjacent springs 150a, 150b that cause the valves 104 to open. A valve guide 100 is used to position the valve 104 within the cylinder head 106.
In general, valve guides and valves are subject to extremely high thermal and mechanical stress. Due to the duty cycle imposed on engines and the possible use of different grades of diesel, the valve guide is subjected to increased levels of acid which condenses thereon, resulting in corrosion and premature failure of the valve guide. More specifically, exhaust gases enter the clearance between the valve and the valve guide during engine operation. The water jacket, which is used to cool the valve and the cylinder head, also cools the exhaust gases causing them to condense. As a result, acid forms between the valve guide and the valve, resulting in corrosion of both the valve and the valve guide.
Diesel engines operating on high sulfur fuels periodically require grinding of the exhaust valves and seats employed therein due to corrosion effects and exposure to high heat levels and the acid formed thereon. Such corrosion tends to induce a channeling or guttering of the valve faces which accelerates such corrosion and gives rise to gas leakage past the valves and potential breakage of the valve heads.
Additionally, valve guides in traditional valve train systems are subject to corrosion due to the acid formed thereon. Previously, a relatively soft metal was used for valve guides in engines. As a result, such valve guides were readily worn and corroded during operation of the engine. Additionally, the acid creates a clearance between a shaft hole of the valve guide and a valve stem which causes an oil-containing gas and smoke to be discharged. As a result, various measures have been taken to prevent the valve guide from being worn and corroded. For example, corrosion resistant Ni-Resist material has been used to prevent valve guide failure. However, due to the increased cost of Nickel, a dominant constituent in the Ni-Resist alloy, the part cost has increased significantly.
Therefore, it is an aspect of the present invention to provide a method for maintaining the surface temperature of the valve guide in order to prevent condensation of acidic gases into acid (e.g., sulfuric acid (H2SO4)) between the valve and the valve guide. This method may include the extension of the valve guide into the exhaust port of the valve train system to increase the surface temperature of the valve guide. Additionally, it is another aspect of the present invention to provide a valve guide including a recess portion to loosen the engagement between the cylinder head wall and the valve guide. This recess portion maintains the surface temperature of the valve guide to prevent condensation of sulfuric acid.
Although a recess portion had been used in prior art, it was used only to fit the valve into the cylinder. The prior art recess portions were not sized and shaped to maintain the surface temperature of the valve. In contrast, the present invention uses a recess portion to control the surface temperature of the valve guide to prevent exhaust gases from condensing to form acid thereon.